An example of a conventional transporting apparatus having a vertically movable holding portion is disclosed in JP 2003-128381A (paragraphs [0014] to [0021], FIGS. 2, 4, 5). This transporting apparatus is provided with a traveling carriage for transporting articles, which is provided with a suspension piece for supporting in a suspended state a holding portion for holding an article, in such a manner that the suspension piece can be freely raised and lowered by a raising and lowering motor, and is provided with control means for controlling actuation of the raising and lowering motor and the holding portion switching operation of switching the holding portion between a holding state and a hold release state such that, with that traveling carriage stopped at a target position for article transfer, the holding portion is raised and lowered and a retrieval operation of retrieving an article loaded on an article station and a release operation of releasing an article on the article station are performed.
That is, the transporting truck is provided with a holding portion supported suspended by a wire, and with the transporting truck stopped at a position above a container retrieval position, the holding portion is raised and lowered by raising and lowering the wire with a drum drive motor, and the holding portion is switched between a state in which a pair of holding pieces are swung toward one another to hold the flange of a transporting container and a state in which the pair of holding pieces are swung away from one another to release their hold on the flange of the transporting container, thereby using the holding portion to retrieve the transporting container from the container retrieval station and release the transporting container at the container retrieval station.
This type of transporting apparatus is provided with a raised/lowered amount detection sensor for detecting the amount that the holding portion has been raised or lowered by the raising and lowering motor, and is configured such that when performing the retrieval operation or the release operation with the holding portion, control is executed to operate the raising and lowering motor based on the information detected by the raised/lowered amount detection sensor, and thus the holding portion is lowered to a target lowering position for switching to the holding state or the hold release state.
In such transporting apparatuses, when for example an abnormality occurs in the setting state of the article loading stand, which forms the article station, and causes a change in the distance from the article station to the path over which the traveling carriage is moved or the suspension piece is extended, then even if based on detection information from the raised/lowered amount detection sensor for detecting the amount that the holding portion is raised or lowered by the raising and lowering motor it is determined that the holding portion is in the target lowering position, in practice there are cases where the holding portion has been lowered too far below the target lowering position. When the holding portion has been lowered too far below the target lowering position, then, for example, the holding chucks of the holding potion come into contact with a portion of the article, making it difficult or impossible for the holding portion to be switched to the holding state or the hold release state.
For this reason, conventionally a configuration has been adopted in which an excess lowering detection sensor is provided for detecting the relative positional relationship in the vertical direction between a holding portion that has been lowered to a target lowering position and an article loaded on the article station to detect whether the holding portion has been lowered too far below the target lowering position, and operation of the transporting apparatus is stopped when this excess lowering detection sensor detects that the holding portion has been lowered too far.